Where can the latest API documentation be found?
Update
You can now use http://www.blender.org/api/blender_python_api_current/ to link to current API documentation. The difference from the old redirect is you can now link to specific parts, search results, etc. on the latest docs.
You can still specify a specific version if needed, e.g.
http://www.blender.org/api/blender_python_api_2_76_2/ goes to the 2.76 specific documentation.

Origonal answer
This url is always redirected to the latest API documentation.
It redirects to http://www.blender.org/documentation/blender_python_api_*version*